A number of techniques have been developed that facilitate the detection of various metallic objects (e.g., unexploded ordnance (UXO)) in the subsurface of the Earth, including magnetometry and pulsed electromagnetism (EM). Magnetometry techniques may include using one or more magnetometers capable of sensing magnetic fields. The magnetometers may be employed to measure disruptions in the Earth's magnetic field due to the presence of metallic objects.
Pulsed EM techniques may include one or more pulsed-induction sensors (also referred to as EM sensors or EM coils). The pulse induction sensors may include one or more coils capable of producing and detecting electromagnetic radiation. For example, an electromagnetic pulse may be generated by the one or more coils, inducing a current in conductive materials such as metallic objects. This induced current produces a secondary magnetic field which may be sensed by the one or more EM coils.
In general, magnetometry techniques perform particularly well for deep subsurface objects containing ferrous metals such as iron, steel, etc., while pulsed EM techniques perform well for shallow subsurface objects containing non-ferrous metal such as brass, aluminum, etc.